There exists a need for a method and apparatus for accurately measuring charge accumulated over a comparatively long period of time, for example 10-100 milliseconds, for use in instruments such as a low level light detector, ion detector, a photodetector, photomultiplier, e-beam detector and piezoelectric charge detector and arrays of such devices. For example, current state of the art mass spectrometers employ ion detector arrays which are hybrids composed of a microchannel electron multiplier array coupled to a phosphor screen which is then coupled to a photodiode array using fiber-optic plate and image format reducer. Due to the cost of the individual components and the added complexity of assembling them together, these detector arrays tend to be relatively expensive. The micro-channel plate also requires a high voltage accelerating field to produce secondary electron multiplication from electrons generated by the initial positive ion impact.